Gas sensor and gas-measuring device for detecting volatile organic compounds

Abstract

A gas sensor 10 has a measuring channel 11 with a gas inlet 12 and with a gas outlet 13 , at least one receptor layer 20 , a reference electrode 30 and a voltage-controlled analysis unit 50 . The reference electrode 30 is capacitively coupled with the receptor layer 20 . The reference electrode 30 is connected to the analysis unit 50 in an electrically conductive manner. The receptor layer 20 is formed in measuring channel 11 . The measuring channel 11 forms a dielectric layer between the receptor layer 20 and the reference electrode 30 . The receptor layer 20 has a support 21 and an analyte-binding layer 22 . The present invention provides for the analyte-binding layer 22 to be a self-assembling monolayer (SAM).

The invention claimed is: 
     
       1. A gas sensing method comprising:
 (a) providing a gas sensor comprising a measuring channel with a gas inlet and with a gas outlet, at least one receptor layer, a reference electrode and an analysis unit wherein the reference electrode is capacitively coupled with the receptor layer, the reference electrode is connected, electrically, to the analysis unit, the receptor layer is formed in the measuring channel, the measuring channel forms a dielectric layer between the receptor layer and the reference electrode, the receptor layer has a support and an analyte-binding layer, the analyte-binding layer is a self-assembling monolayer, which is comprised of a plurality of molecules, the plurality of molecules each having the general formula R1-R2-X wherein R1 is a coupling group, selected from the group consisting of sulfide, disulfide, sulfinyl, sulfino, sulfo, carbonothiol, thiosulfate, thiocyanate, isothiocyanate, and wherein the molecules of the self- assembling monolayer are coupled each via R1 to the support, the support is a layer comprised of metal, the metal is selected from the group consisting of gold, platinum, palladium, silver and copper, wherein R2 is a spacer, selected from the group consisting of alkane, alkene, alkyne, heteroalkane, heteroalkene, heteroalkyne, substitute alkanes, substituted alkenes, substituted alkynes, substituted heteroalkanes, substituted heteroalkenes, substituted heteroalkynes, ethers, amines and X is an organic or organometallic group with at least one delocalized π system, wherein X is coupled directly to the spacer R2 via a covalent bond between the spacer R2 and a member of the at least one delocalized π system; and 
 (b) directing a gas to be tested comprising at least one volatile organic compound into the measuring channel through the gas inlet; 
 (c) measuring a change in capacitance between the reference electrode and the receptor layer over a first period of time; and 
 (d) calculating a concentration of the at least one volatile organic compound of the first gas as a function of the measured change in capacitance. 
 
     
     
       2. The method of  claim 1 , wherein step (c) further comprises allowing intermolecular interactions between the at least one volatile organic compound and the at least one delocalized π system to move at least one π electron in the at least one delocalized π system, resulting in a shift in a dipole moment of the delocalized π system. 
     
     
       3. The method of  claim 2 , wherein step (c) further comprises transmitting the shift in dipole moment of the delocalized π system to the support via the spacer and the coupling group, resulting in a change in work function on the support. 
     
     
       4. The method of  claim 3 , wherein step (c) further comprises measuring the change in work function on the support using the analysis unit. 
     
     
       5. The method of  claim 1 , wherein step (c) further comprises measuring the change in capacitance between the reference electrode and the receptor layer over the first period of time, the measured change in capacitance being a result of intermolecular interactions between the at least one volatile organic compound and the analyte binding layer. 
     
     
       6. The method of  claim 1 , further comprising:
 (e) directing a calibration gas comprising a known concentration of at least one volatile organic compound into the measuring channel through the gas inlet; 
 (f) measuring a change in capacitance between the reference electrode and the receptor layer over a second period of time; and 
 (g) adjusting the function used in step (d) to calculate the concentration of the at least one volatile organic compound of the first gas based on the change in capacitance measured in step (f) and the known concentration of the at least one volatile organic compound in the calibration gas. 
 
     
     
       7. The method of  claim 1 , wherein step (b) further comprises directing the gas to be tested comprising the at least one volatile organic compound into the measuring channel through the gas inlet, the at least one volatile organic compound comprising benzene. 
     
     
       8. The method of  claim 1 , wherein step (b) further comprises directing the gas to be tested comprising the at least one volatile organic compound through the measuring channel between the receptor layer and the reference electrode, causing the gas to be measured to act as a dielectric layer in a capacitor formed between the receptor layer and reference electrode. 
     
     
       9. The method of  claim 1 , wherein step (b) further comprises heating the measuring channel. 
     
     
       10. The method of  claim 1 , wherein step (c) further comprises measuring the change in capacitance between the reference electrode and the receptor layer over the first period of time using the analysis unit, the analysis unit comprising a voltage-controlled oscillator. 
     
     
       11. The method of  claim 1 , further comprising:
 (h) performing wherein steps (b) through (d) while the gas sensor is being worn on a person as a personal air monitor (PAM).